CN114539451A

CN114539451A - Hydroxyl-rich single-ion conductor polymer SPVA-Li and preparation method and application thereof

Info

Publication number: CN114539451A
Application number: CN202210233377.6A
Authority: CN
Inventors: 张运丰; 胡振原; 蔡卫卫; 杨泽惠
Original assignee: China University of Geosciences
Current assignee: China University of Geosciences
Priority date: 2022-03-09
Filing date: 2022-03-09
Publication date: 2022-05-27
Anticipated expiration: 2042-03-09
Also published as: CN114539451B

Abstract

The invention discloses a hydroxyl-rich single-ion conductor polymer SPVA-Li and a preparation method and application thereof. The preparation method comprises the steps of firstly preparing a hydroxyl-rich single-ion conductor polymer SPVA-Li through a two-step method, and then introducing the SPVA-Li into a PEO matrix through a solution casting method to prepare the composite solid polymer electrolyte SPVA-Li SPEs. The obtained SPVA-Li SPEs have good mechanical properties and electrochemical properties. Meanwhile, hydroxyl on the SPVA-Li chain segment and ether bond on the PEO chain segment have hydrogen bond interaction, so that crystallization of the polymer chain segment can be effectively inhibited, the interaction between lithium ions and the ether bond can be weakened, and the SPVA-Li SPEs prepared by the method have better ionic conductivity and lithium ionsNumber of migration, excellent mechanical properties and thermal stability. Therefore, the Li/Li symmetrical battery prepared based on the SPVA-Li SPEs can stably run for 400h without short circuit. Further, LiFePO₄the/Li cell can be cycled stably for 100 cycles at 0.2C and 0.5C rates. Therefore, the SPVA-Li of the invention has great potential in the practical application of solid-state lithium metal batteries.

Description

Hydroxyl-rich single-ion conductor polymer SPVA-Li and preparation method and application thereof

Technical Field

The invention belongs to the technical field of high molecular materials, and particularly relates to a hydroxyl-rich single-ion conductor polymer SPVA-Li, a preparation method and application thereof, in particular to application of SPVA-Li as a polymer filler in preparation of composite solid polymer electrolytes and dendrite-free lithium metal batteries.

Background

At present, with the increasing growth of portable devices, electric vehicles and large-scale energy storage devices, the demand for rechargeable batteries with high safety and high energy density is increasing. Lithium metal batteries use lithium negative electrodes due to their high theoretical capacity (3860mAh g) compared to other types of batteries^-1) And the lowest electrochemical potential (-3.04V vs. standard hydrogen electrode), have been widely recognized by researchers as an ideal next generation high energy density negative electrode material. However, lithium metal is highly reactive with liquid electrolytes to produce uncontrollable lithium dendrites. Sharp lithium dendrites may puncture the separator, causing a short circuit in the cell. In addition, the inherent flammability and poor thermal stability of organic liquid electrolytes can cause catastrophic cell combustion and even explosion. The nonflammability and high thermal stability of the solid electrolyte are effective in reducing the above-mentioned problems, as compared with the liquid electrolyte. Therefore, based on the above, replacing flammable liquid electrolyte with solid electrolyte with better thermal stability has been widely considered by scientists as an effective solution for constructing high-safety lithium metal batteries.

Generally, solid electrolytes fall into two broad categories: inorganic solid electrolytes and polymer solid electrolytes. For inorganic solid electrolytes, these are usually composed of sulfides (e.g., Li)₁₀GeP₂S₁₂) And oxides (such as: olivine type, perovskite type, NASICON type, and LiPON type), which have high ionic conductivity and excellent thermal stability. However, the high interfacial internal resistance and poor film-forming property limit the practical application of solid electrolytes. In contrast, the polymer solid electrolyte is composed of lithium salt and polymer matrix, and has light weight, easy processing and flexibilityGood performance and the like, and can be used as a key component of a high-safety battery. Among polymer matrices, polyethylene oxide electrolytes (PEO SPEs) have attracted much attention since Wright's discovery, due to their advantages of good compatibility with lithium salts, easy processing, low price, and the like. However, due to the high crystallinity of PEO, the produced SPEs have lower ionic conductivity, poorer lithium ion transport number and electrochemical performance, which limit the application in solid state lithium metal batteries (fig. 1). Accordingly, there is a significant need for a method to address the above-mentioned disadvantages of PEO SPEs.

The incorporation of advanced organic polymeric materials (e.g., polyacrylonitrile, polyionic liquids, single ion conductors) or inorganic fillers (e.g., SiO) into PEO matrices₂,MOFs,g-C₃N₄) The formed composite solid electrolyte can effectively reduce the crystallinity of the polymer, thereby improving the amorphous region of the polymer and being beneficial to the conduction of lithium ions. However, most inorganic fillers are more difficult to disperse uniformly in a PEO matrix due to their easily aggregated nature.

For the above reasons, the present application has been made.

Disclosure of Invention

In view of the above-mentioned problems or drawbacks of the prior art, the applicant believes that blending an organic polymer filler in a PEO matrix is a simple method for preparing a composite solid polymer electrolyte. The single-ion conductor electrolyte is used as a novel polymer, has repeated anion units on a high molecular chain segment, has a lithium ion migration number close to 1, excellent mechanical properties, good thermal stability and higher ionic conductivity, and can be used as an advanced polymer filler for preparing a PEO-based composite polymer electrolyte.

Based on the above reasons, the present invention aims to provide a hydroxyl-rich single-ion conductor polymer SPVA-Li, a preparation method and applications thereof, which solve or at least partially solve the above technical defects in the prior art.

In order to achieve one of the above objects of the present invention, the present invention adopts the following technical solutions:

a preparation method of a hydroxyl-rich single-ion conductor polymer SPVA-Li specifically comprises the following steps:

dissolving polyvinyl alcohol (PVA) in deionized water to obtain a PVA solution; then adding disodium 4-formylbenzene-1, 3-disulfonate (BADS) and hydrochloric acid aqueous solution into the PVA solution according to the mixture ratio, and uniformly mixing; heating the obtained mixed reaction liquid to 65-75 ℃, stirring and reacting for 36-60 h; after the reaction is finished, cooling, precipitating, washing and vacuum drying the obtained product; and completely converting the dried product into SPVA through cation exchange resin, and lithiating, precipitating, washing and drying the product after drying again to obtain the single-ion conductor polymer SPVA-Li rich in hydroxyl.

Further, in the above technical solution, the amount of the deionized water may not be specifically limited as long as PVA can be completely dissolved, and for example, the amount ratio of the PVA to the deionized water may be (1 to 10) parts by mass: (50-200) parts by volume, wherein: the mass portion and the volume portion are as follows: ml is used as a reference.

Further, in the technical scheme, the polyvinyl alcohol is preferably dissolved by heating for 4-8 hours at the temperature of 80-100 ℃.

Further, according to the technical scheme, the mass ratio of the polyvinyl alcohol to the disodium 4-formylbenzene-1, 3-disulfonate is 1: 1.5 to 2.

Specifically, in the above technical scheme, the hydrochloric acid aqueous solution functions as a catalyst in the above reaction, and the amount of the hydrochloric acid aqueous solution is small. Preferably, the dosage ratio of the polyvinyl alcohol to the hydrochloric acid aqueous solution is 1 part by mass: (1-5) parts by volume; more preferably 1 part by mass: 2 parts by volume, wherein: the mass portion and the volume portion are as follows: ml is used as a reference.

Further, in the above technical scheme, the reaction temperature of the mixed reaction solution is preferably 70 ℃, and the stirring reaction time is preferably 48 hours.

Further, according to the technical scheme, the vacuum drying temperature is preferably 60-80 ℃, and the drying time is preferably 12-36 h.

Further, in the above technical scheme, the specific implementation process for completely converting the cation exchange resin into SPVA is as follows:

dissolving the dried product in deionized water at room temperature to obtain a solution, and pouring the solution into a container containing-SO₃And converting Na ions in the product into H ions by using a reduced pressure column of the H strong acid type cationic resin, precipitating and separating a solution obtained by conversion in absolute ethyl alcohol, and drying in vacuum to obtain the SPVA.

Further, in the above technical scheme, the process adopted by the lithiation is specifically as follows:

and (3) reacting the dry SPVA with an equimolar amount of lithium hydroxide in water for 24 hours.

The second purpose of the invention is to provide the hydroxyl-rich single-ion conductor polymer SPVA-Li prepared by the method.

The third purpose of the invention is to provide a composite solid polymer electrolyte SPVA-Li SPEs, wherein the SPVA-Li SPEs are prepared by a solution casting method of viscous solution containing SPVA-Li, and the preparation method comprises the following specific steps:

adding dried polyethylene oxide (PEO), lithium bistrifluoromethylsulfonate (LiTFSI) and a hydroxyl-rich single-ion conductor polymer SPVA-Li into deionized water, and uniformly stirring to obtain a uniform viscous solution; and then pouring the viscous solution in a grinding tool, and drying after pouring to obtain the composite solid polymer electrolyte SPVA-Li SPEs.

Further, according to the technical scheme, the mass ratio of the SPVA-Li to the PEO is 5-20: 100, more preferably 15: 100.

further, in the above technical solution, the mass ratio of LiTFSI to PEO is that LiTFSI plays a role in the present invention:

the molar ratio of repeating units (i.e., EO) of LiTFSI to PEO in the present invention is fixed at 20:1, where LiTFSI is an organic electrolyte lithium salt that functions as a lithium source in the electrolyte, primarily supplying lithium ions to the electrolyte.

Further, in the technical scheme, in the composite solid polymer electrolyte SPVA-Li SPEs, EO and Li⁺Preferably 20: 1.

Further, according to the technical scheme, the grinding tool is preferably a tetrafluoroethylene grinding tool.

Further, in the above technical solution, the drying is preferably performed in two steps: drying was first carried out on a hot plate at 50 ℃ for 12h and subsequently in a vacuum oven at 50 ℃ for 12 h.

The fourth purpose of the present invention is to provide the application of the composite solid polymer electrolyte in a dendrite-free lithium metal battery or a solid lithium metal battery.

Further, in the above technical solution, the solid-state lithium metal battery includes a Li/Li symmetric battery or LiFePO₄a/Li cell.

A dendrite-free lithium metal battery or a solid lithium metal battery comprising the above composite solid polymer electrolyte.

Compared with the prior art, the invention has the following beneficial effects:

the invention firstly prepares the single ion conductor polymer SPVA-Li rich in hydroxyl through a two-step method, and then introduces the polyvinyl alcohol lithium sulfonate (SPVA-Li) into a PEO matrix through a simple solution pouring method capable of large-scale preparation to prepare the composite solid polymer electrolyte (SPVA-Li SPEs). The obtained SPVA-Li SPEs have good mechanical properties and electrochemical properties. More importantly, hydroxyl on the SPVA-Li chain segment and ether bond on the PEO chain segment have hydrogen bond interaction, can effectively inhibit crystallization of the polymer chain segment and weaken interaction of lithium ions and the ether bond, so that the prepared SPVA-Li SPEs have better ionic conductivity and lithium ion migration number (1.76 multiplied by 10)^-4S cm^-1And 0.59), significantly higher than the SPVA-Li free PEO SPEs (1.03X 10)^-4S cm^-1And 0.39). In addition, the hydrogen bond crosslinking structure can effectively improve the mechanical property and the thermal stability of the SPVA-Li SPEs. Therefore, the Li/Li symmetrical battery prepared based on the SPVA-Li SPEs can stably run for 400h without short circuit. Further, LiFePO₄the/Li cell can be cycled stably at 0.2C and 0.5C rates for 100 cycles. Therefore, the novel solid polymer electrolytes disclosed in the present invention have great potential for practical application in solid lithium metal batteries.

Drawings

FIG. 1 is a schematic illustration of the composition, mechanism of SPVA-Li SPEs and PEO SPEs of the present invention;

in fig. 2: (a) a synthetic route of SPVA-Li; (b) nuclear magnetic spectrum of SPVA-Li; (c) XRD patterns of PVA and SPVA-Li; (d) schematic preparation of SPVA-Li SPEs;

in fig. 3: (a, b) flexible picture display of 15% SPVA-Li SPEs; (c, d) SEM picture of 15% SPVA-Li, (c) is surface picture, (d) is cross-sectional view; (e) distribution test of S element in EDX of 15% SPVA-Li/PEO film prepared in comparative example 2. (f-h) O, F, C element distribution test in 15% SPVA-Li SPEs EDX; (i) ion conductivity measurements of PEO SPEs prepared in comparative example 1 and different levels of SPVA-Li SPEs; (j) XRD testing of PEO, PEO SPEs, 15% SPVA-Li SPEs; (k) PEO, PEO SPEs, 15% SPVA-Li SPEs DSC test;

in fig. 4: (a) stress strain curves for PEO SPEs and 15% SPVA-Li SPEs; (b) photographs of 15% SPVA-Li SPEs original and 1800.0% stretched; (c) thermal stability test pictures of PP film, PEO SPEs, and 15% SPVA-Li SPEs; (d) LSV curves for PEO SPEs and 15% SPVA-Li SPEs; (e) 15% SPVA-Li SPEs lithium ion transport number test (inset: EIS test before and after CA); (f) PEO SPEs lithium ion transport number test (inset: EIS test before and after CA);

in fig. 5: (a) 15% SPVA-Li SPEs at 25 μ A cm^-2And 50. mu.A cm^-2Testing constant current polarization voltage under current density; (b) PEO SPEs at 25 μ A cm^-2And 50. mu.A cm^-2Testing constant current polarization voltage under current density; (c-e) SEM pictures of lithium metal disassembled after cycling of the Li/15% SPVA-Li SPEs/Li battery for 400h and the Li/PEO SPEs/Li battery for short circuit, where (c) and (e, f) are cross-sectional and surface pictures, respectively, of lithium metal after cycling of the battery based on the 15% SPVA-Li SPE, (d) and (h, i) cross-sectional and surface pictures of lithium metal after cycling of the battery based on the PEO SPE;

in fig. 6: (a) LiFePO₄EIS spectrum of/15% SPVA-Li SPEs/Li cell (inset: LiFePO)₄Equivalent circuit of Li battery); (b) LiFePO₄15% SPVA-Li SPEs/Li and LiFePO₄A rate test plot of/PEO SPEs/Li at 0.1C-1C; (c) LiFePO₄15% SPVA-Li SPEs/Li and LiFePO₄PerPEO SPEs/Li batteryLong-term cycling of the cell at 0.2C; (d) LiFePO₄15% SPVA-Li SPEs/Li and LiFePO₄Long-term cycling test at 0.5C for a PEO SPEs/Li cell; the above tests were all carried out at a temperature of 60 ℃;

FIG. 7 is an FTIR spectrum of PVA and SPVA-Li in example 1 of the present invention;

FIG. 8 is an EIS spectrum from 25-80 ℃ of 15% SPVA-Li SPEs prepared in example 4;

FIG. 9 is a DSC spectra of pure PEO, PEO SPEs prepared in comparative example 1, and 15% SPVA-Li SPEs prepared in example 4;

FIG. 10 is an FTIR spectrum of the SPVA-Li prepared in example 1 and 15% SPVA-Li/PEO (without LiTFSI) composite prepared in comparative example 2;

FIG. 11 is a TGA plot of the PEO SPEs prepared in comparative example 1 and the 15% SPVA-Li SPEs prepared in example 3 of the present invention;

FIG. 12 is an SEM surface view of a lithium plate before cycling;

in fig. 13: (a) LiFePO₄A 5 th circle capacity-voltage curve chart of a 15% SPVA-Li SPEs/Li battery under different multiplying power; (b) LiFePO₄Capacity vs. Voltage plot at 5 th cycle for various rates of the/PEO SPEs/Li cell.

Detailed Description

The present invention will be described in further detail below with reference to examples. The present invention is implemented on the premise of the technology of the present invention, and the detailed embodiments and specific procedures are given to illustrate the inventive aspects of the present invention, but the scope of the present invention is not limited to the following embodiments.

The equipment and raw materials used in the present invention are commercially available or commonly used in the art. The raw materials used in the following examples are as follows: disodium 4-formylbenzene-1, 3-disulfonate (BADS), polyvinyl alcohol (PVA1799, 99% hydrolyzed), lithium bistrifluoromethylsulfonate (LiTFSI, 99%), lithium hydroxide (LiOH H;)₂0, 99%), polyethylene oxide (PEO, M)_w600000 g/mol), N-methyl-2-pyrrolidone (NMP, 98%), ethanol (99.9%) and HCl solution (37% in H)₂0) Purchased from alatin corporation. P (VDF-HFP) is available from Sigma. Acetylene black and lithium iron phosphate purchased from KongjinggiAnd (4) a driver. Celgard 2400 membranes were purchased from Celgard corporation. Lithium tablets were purchased from energy companies in china. The water used was deionized water.

The methods in the following examples are conventional in the art unless otherwise specified.

The characterization and electrochemical performance test methods involved in the following examples of the invention are as follows:

the nuclear magnetic test is to adopt¹H NMR 400MHz instrumentation (AVANCE III HD 400MHz, Swiss BRUKER). The surface morphology of the samples was measured by scanning electron microscopy (FE-SEM, SU8010, HITACHI). Fourier Infrared Spectroscopy was measured by FTIR-6700(Nicolet iS 50). Thermogravimetric analysis was performed using a thermogravimetric analyzer (STA 409PC, Germany NETZSCH) under the following test conditions: under nitrogen atmosphere at 10 deg.C for min^-1The temperature is raised. The differential scanning calorimeter was tested using (METTLER TOLEDO DSC3) under the following conditions: under nitrogen atmosphere at 10 deg.C for min^-1The temperature is raised and lowered. The X-ray diffractometer adopts D5005 Bruker AXS to carry out testing under the following conditions: λ 1.5140, voltage 40kV, scan range: 5-60 degrees. The mechanical properties of the material were measured using a tensile tester (XWL (PC)) at a tensile speed of 25mm min^-1And (6) carrying out testing.

The conductivity is measured by firstly assembling a polymer solid electrolyte between two steel sheets to form a symmetrical battery, and then measuring an AC impedance spectrogram by using an electrochemical workstation (PGSTAT), wherein the conductivity (sigma) is as follows:

wherein L represents the thickness of the electrolyte, R_bThe internal resistance of the electrolyte is represented, and S represents the area of the electrolyte.

Crystallinity (χ) of solid polymer electrolyte_c) Is calculated by the following formula:

wherein, Δ H_mRepresentative is the enthalpy of fusion, Δ H, of the solid polymer electrolyte_PEOIs a melting enthalpy of 100% crystalline PEO (196.4J g)^-1)，f_PEOIs the mass fraction of PEO in the solid electrolyte.

Transference number of lithium ion

The Li/Li battery is assembled by solid polymer electrolyte, then the test is carried out by a steady-state current method, and the numerical value is calculated by a Bruce-Vincent-Evans formula:

where Δ V is the applied polarization voltage (10mV), I₀And I_sIs the initial and steady state current, R, of the battery test₀And R_sAre the initial and steady state resistances of the battery test.

The electrochemical stability window is the assembly of the samples into a Li/Steel Sheet (SS) cell, then tested by linear sweep voltammetry, test conditions: the scanning speed is 1mV s^-1The scanning voltage is 0-6V.

Rate performance and cycling performance of the cells were tested and analyzed in a blue test system (CT2001, wuhan) with electrolyte assembly of 2025 type cells.

LiFePO referred to in the examples below₄The preparation method of the positive electrode comprises the following steps:

adding active material (LiFePO)₄) Mixing conductive agent carbon black (Super-P) and binder PVDF (4 wt.% of NMP solution) together according to a mass ratio of 7:2:1, fully stirring and carrying out ultrasonic treatment to ensure that all substances are completely dispersed to obtain electrode material slurry, uniformly coating the slurry on the surface of a smooth aluminum foil by using a scraper, placing the electrode in a vacuum oven at 100 ℃ after the solvent is primarily volatilized, drying for 36 hours, cutting the electrode into circular electrode plates with the diameter of 14mm after drying, and keeping the loading amount of active substances of each circular electrode plate at 1.5mg cm^-2In the meantime.

Example 1

The hydroxyl-rich single-ion conductor polymer SPVA-Li of the embodiment is prepared by the following method, and the method specifically comprises the following steps:

the detailed synthesis procedure of SPVA-Li is shown in FIG. 2. PVA (5g) was added to 100ml of deionized water and heated at 90 ℃ for 6h to dissolve completely. Subsequently, BADS (8.8g, 28.4mmol) and HCl solution (10ml) were added to the above PVA solution, followed by stirring at 70 ℃ for 48 h. After the reaction was completed, the solution was cooled to room temperature, and then it was poured into an anhydrous ethanol solution (1500ml) for precipitation, and the precipitate was washed 3 times with an anhydrous large amount of ethanol and dried in a vacuum oven at 70 ℃ for 24 hours. 5g of the product obtained was dissolved in deionized water to prepare a solution having a concentration of 20mg ml^-1The aqueous solution of (a); then pouring the solution into a container with-SO₃And converting Na ions in the product into H ions by using a reduced pressure column of the H strong acid type cationic resin, precipitating the obtained converted solution in 500ml of absolute ethanol, and drying the obtained precipitate at the temperature of 80 ℃ in vacuum for 24H to obtain the SPVA. And then reacting the obtained SPVA with lithium hydroxide with equal molar quantity in water for 24h, then precipitating in 500ml of absolute ethyl alcohol, washing for three times (each time with 500ml of absolute ethyl alcohol), and drying at 80 ℃ in vacuum for 24h to obtain the final product SPVA-Li. The grafting density of BDSA in SPVA-Li was calculated by nuclear magnetic software to be about 18% (molar ratio of BADS to hydroxyl of repeating unit in PVA).

Example 2

A composite solid polymer electrolyte 5% SPVA-Li SPEs (wherein 5% represents the feeding mass ratio of SPVA-Li to PEO) of this example was prepared by the following method, which specifically includes the following steps:

LiTFSI and PEO were dried in a vacuum oven at 60 ℃ for 24h before use. The SPVA-Li SPEs are prepared by a solution casting method. Specifically, 1g of PEO, 0.33g of LiTFSI, and 0.05g of SPVA-Li were added to a 15ml beaker of ionized water and stirred at room temperature for 12 hours until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at the temperature of 50 ℃ on a heating plate, and then drying for 12 hours at the temperature of 50 ℃ in a vacuum oven to obtain 5% SPVA-Li SPEs. Wherein: the molar ratio of monomer (EO) of PEO to LiTFSI was fixed at 20: 1.

Example 3

A composite solid polymer electrolyte 10% SPVA-Li SPEs (wherein 10% represents the feeding mass ratio of SPVA-Li to PEO) of this example was prepared by the following method, specifically including the following steps:

LiTFSI and PEO were dried in a vacuum oven at 60 ℃ for 24h before use. The SPVA-Li SPEs are prepared by a solution casting method. Specifically, 1g of PEO, 0.33g of LiTFSI, and 0.1g of SPVA-Li were added to a beaker containing 15ml of ionized water, and stirred at room temperature for 12 hours until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at the temperature of 50 ℃ on a heating plate, and then drying for 12 hours at the temperature of 50 ℃ in a vacuum oven to obtain the 10% SPVA-Li SPEs. Wherein: the molar ratio of monomer (EO) of PEO to LiTFSI was fixed at 20: 1.

Example 4

A composite solid polymer electrolyte 15% SPVA-Li SPEs (wherein 15% represents the feeding mass ratio of SPVA-Li to PEO) of this example was prepared by the following method, specifically including the following steps:

LiTFSI and PEO were dried in a vacuum oven at 60 ℃ for 24h before use. The SPVA-Li SPEs are prepared by a solution casting method. Specifically, 1g of PEO, 0.33g of LiTFSI, and 0.15g of SPVA-Li were added to a beaker containing 15ml of ionized water, and stirred at room temperature for 12 hours until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at the temperature of 50 ℃ on a heating plate, and then drying for 12 hours at the temperature of 50 ℃ in a vacuum oven to obtain the 15% SPVA-Li SPEs. Wherein: the molar ratio of monomer (EO) of PEO to LiTFSI was fixed at 20: 1.

Example 5

A composite solid polymer electrolyte of this example, 20% SPVA-Li SPEs (where 20% represents the SPVA-Li to PEO charge mass ratio), was prepared using the following method, which specifically included the following steps:

LiTFSI and PEO were dried in a vacuum oven at 60 ℃ for 24h before use. The SPVA-Li SPEs are prepared by a solution casting method. Specifically, 1g of PEO, 0.33g of LiTFSI, and 0.2g of SPVA-Li were added to a beaker containing 15ml of deionized water, and stirred at room temperature for 12 hours until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at 50 ℃ by a heating plate, and then drying for 12 hours at 50 ℃ in a vacuum oven to obtain the 20% SPVA-Li SPEs. Wherein: the molar ratio of monomer (EO) of PEO to LiTFSI was fixed at 20: 1.

Comparative example 1

The polyethylene oxide electrolyte (PEO SPEs) of this comparative example was prepared by substantially the same method as in example 2, except that: no SPVA-Li was added to this comparative example. The specific preparation method of the polyethylene oxide electrolyte (PEO SPEs) of this comparative example is as follows:

LiTFSI and PEO were dried in a vacuum oven at 60 ℃ for 24h before use. PEO SPEs are prepared by solution casting. Specifically, 1g of PEO, 0.33g of LiTFSI was added to a 15ml deionized water beaker and stirred at room temperature for 12h until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at 50 ℃ of a heating plate, and then drying for 12 hours at 50 ℃ in a vacuum oven to obtain the PEO SPEs. Wherein: the molar ratio of monomer (EO) of PEO to LiTFSI was fixed at 20: 1.

Comparative example 2

The preparation method of the 15% SPVA-Li/PEO (without LiTFSI) film of this comparative example is as follows:

the 15% SPVA-Li/PEO (without LiTFSI) film was prepared by solution casting. Specifically, 1g of PEO and 0.15g of SPVA-Li were added to a 15ml deionized water beaker and stirred at room temperature for 12h until the drug was completely dissolved. And then pouring the prepared solution with certain viscosity into a polytetrafluoroethylene grinding tool, drying for 12 hours at 50 ℃ of a heating plate, and then drying for 12 hours at 50 ℃ in a vacuum oven to obtain the 15% SPVA-Li/PEO film.

And (3) testing the structure and the performance:

the structure and performance of SPVA-Li and SPVA-Li SPEs are characterized in that:

as shown in FIG. 2a, the novel hydroxyl-rich single-ion conductor polymer SPVA-Li of example 1 can be synthesized by a two-step method. First, PVA and BADS react to form SPVA under hydrochloric acid as catalyst, and then-SO is passed through cation exchange resin₃Complete conversion of Na to-SO₃H. Next, the SPVA thus obtained was mixed with an equimolar amount of LiOH H₂Carrying out lithiation reaction on O to obtain SPVA-Li. The invention adopts infrared and nuclear magnetism characterization to prove the successful preparation of SPVA-Li. FIG. 7 is an infrared characterization of SPVA-Li, which can be seen at 1185cm^-1Is the antisymmetric telescopic peak of S ═ O, which indicates that BADS has been successfully grafted onto PVA polymers. FIG. 2b further identifies the chemical structure of SPVA-Li. H_a、H_bAnd H_cBelongs to the benzene ring structure on BADS, H_dAnd H_eBelonging to the PVA structure. In addition, by calculating H_cAnd H_dThe area ratio of (A) to (B), i.e., the molar ratio of the BADS molecules relative to the PVA monomer, gives a grafting yield of BADS on PVA of 18%. The crystallization properties of PVA and SPVA-Li were analyzed by XRD. As shown in FIG. 2c, the sharp peak appearing at 2. theta. of 19.6 ℃ corresponds to the crystal plane of PVA (101), however, the peak intensity of the SPVA-Li polymer at that point is significantly reduced, and the peak width becomes large. The results indicate that SPVA-Li has lower crystallinity than PVA, and facilitates the promotion of lithium ion migration to improve conductivity. The preparation of the SPVA-Li SPEs composite solid state polymeric polyelectrolyte is shown in FIG. 2 d. SPVA-Li, PEO and LiTFSI were dissolved in a certain amount of water and stirred well to form a homogeneous solution. And then pouring the prepared solution into a polytetrafluoroethylene grinding tool by using a solution pouring method, and drying and volatilizing the redundant solvent. Finally, by adjusting the mass ratio of SPVA-Li to PEO (5%, 10%, 15%, 20%), a series of SPVA-Li composite solid polymer electrolytes with different mass fractions, namely 5% SPVA-Li SPEs, 10% SPVA-Li SPEs, 15% SPVA-Li SPEs and 20% SPVA-Li SPEs, respectively, were prepared. For comparison, PEO SPEs without SPVA-Li were prepared in the same manner as the experimental control. In addition, EO and Li are present throughout the solid polymer system⁺In a molar ratio of 20: 1.

FIG. 3a is an optical photograph of 15% SPVA-Li SPEs, which can be found to indicate a smoother and more uniform, and overall translucent state. In addition, the electrolyte membrane can be bent arbitrarily without breaking, indicating that it has excellent flexibility (fig. 3 b). Further characterization by SEM (fig. 3c) found that the surface of the electrolyte membrane was still very flat and uniform on a microscopic scale, and the electrolyte thickness was only 120um thin. EDS spectroscopy can analyze the uniformity of mixing of multiple components very intuitively. FIG. 3e is the EDS sulfur spectrum of a 15% SPVA-Li/PEO (without LiTFSI) membrane, showing that the distribution of the S element is very uniform throughout the system of the membrane, indicating that both SPVA-Li and PEO components have excellent compatibility. In addition, EDS oxygen, fluorine and carbon spectrum testing of 15% SPVA-Li SPEs further indicates that the elements O, F and C are equally distributed throughout the electrolyte very uniformly, indicating that SPVA-Li, PEO and LiTFSI are well compatible and do not phase separate.

The conductivity of the polymer is a very important electrochemical property that determines the performance of the assembled battery. The conductivity can be obtained by measuring electrochemical impedance spectroscopy and then calculating according to the formula (1). The invention tests the conductivity of SPVA-Li SPEs doped with different mass fractions at 25-80 ℃, and the EIS spectrogram results of the 15% SPVA-Li SPEs at different temperatures are shown in figure 8. As shown in FIG. 3i, as the content of SPVA-Li increases, the corresponding electrolyte shows a tendency of increasing first and then decreasing at different temperatures, and the conductivity is maximum at a content of SPVA-Li of 15%. In addition, it was found that the conductivity increased with increasing temperature, since the polymer had better segmental mobility at higher temperatures. 15% SPVA-Li SPEs have ionic conductivities of 1.25X 10 at 25 ℃ and 60 ℃, respectively^-5S cm^-1And 1.76X 10^-4Significantly higher than the control PEO SPEs at 25 deg.C (6.32X 10)^-6S cm^-1) And 60 deg.C (1.03X 10)^-4) The electrical conductivity of (b). The main reason for improving the ionic conductivity of 15% SPVA-Li SPEs is that the SPVA-Li polymeric filler can effectively reduce the crystallinity of a PEO chain segment, thereby increasing the amorphous region of PEO and being beneficial to Li⁺Is being migrated. To confirm the above hypothesis, the present invention characterizes the crystalline properties of the sample using XRD and DSC tests. As shown in FIG. 3j, the XRD pattern of pure PEO showed two very sharp peaks at 19 and 23, corresponding to PEO crystalsThe (120) and (112) crystal planes of (a). The above results indicate that PEO has strong crystallinity at room temperature. The crystallinity of the PEO SPEs is significantly reduced after addition of the LiTFSI, which has a plasticizing effect. In contrast, the 15% SPVA-Li SPEs have the smallest intensity of the characteristic peak on the PEO crystal plane, indicating that doping SPVA-Li in the PEO SPEs system can effectively reduce the crystallinity of PEO. The crystallinity of the polymer was calculated by DSC measurement according to the formula (2). The 15% SPVA-Li SPEs have a crystallinity of only 29.0%, significantly lower than that of PEO SPEs (61.8%), which is consistent with the conclusions from XRD. In addition, the glass transition temperature (T) of pure PEO can be found from the DSC spectrum_g) And melting point (T)_m) At-52.1 and 65.2 deg.c, respectively. In contrast, in the PEO SPEs system formed after addition of LiTFSI, the T of PEO_gIncreasing the temperature from the original-52.1 ℃ to-32.8 ℃ and increasing the temperature T_mThe temperature is reduced from the original 65.2 ℃ to 54.3 ℃. The above results are due to the fact that the strong coordination of LiTFSI and PEO increases the T of PEO_gWhile the plasticizing effect of LiTFSI reduced the T of PEO_m. For comparison, T of 15% SPVA-Li SPEs_gAnd T_mAt-34.8 and 53.6 deg.C, respectively, below the values of PEO SPEs under the same conditions. Considering that the hydroxyl groups of the SPVA-Li molecules and the ether groups of the PEO molecules in the 15% SPVA-Li SPEs system form hydrogen bonding interactions that cause the PEO molecular chains to rearrange and become disordered, the crystallinity is reduced and the T is reduced compared to the PEO SPEs_gAnd T_m. To demonstrate hydrogen bonding interactions on the SPVA-Li and PEO, the FT-IR test characterized the pure SPVA-Li sample and a 15% SPVA-Li/PEO film (without LiTFSI) whose spectra are shown in FIG. 10. The hydroxyl stretching vibration peak of the pure SPVA-Li is 3417cm at wave number^-1Whereas the hydroxyl stretching vibration peak for the 15% SPVA-Li/PEO film shifted to a high wavenumber of 3454, and the results are consistent with the previously reported literature. Thus, the above results indicate that there is a hydrogen bonding interaction between SPVA-Li and PEO, and that this interaction can weaken PEO from Li⁺So that more Li can be released and transported⁺. In addition, the 15% SPVA-Li SPEs also have lower crystallinity and T_mLikewise, the movement of the chain segments and Li are also favored⁺Thereby increasing dissociationThe sub-conductivity.

Characterization of mechanical Properties and thermal stability of (II) solid-State polyelectrolyte

The solid polymer electrolyte has excellent mechanical properties that facilitate battery assembly and lithium dendrite suppression. The mechanical properties of the SPVA-Li SPEs and PEO SPEs were tested by tensile testing and the stress strain curves are shown in FIG. 4 a. The 15% SPVA-Li SPEs have tensile strengths up to 0.65MPa, extremely high elongation at break (1800.0%), and excellent toughness (9.5MJ m)^-3). These properties are 2.8, 4.3, and 8.6 times greater, respectively, than PEO SPEs (Table 1). FIG. 4b is a visual before and after stretching of the 15% SPVA-Li SPEs, and these characterizations clearly demonstrate that the 15% SPVA-Li SPEs have superior mechanical properties to the PEO SPEs, since the SPVA-Li and PEO have hydrogen bonding interactions, thereby improving the mechanical properties of the 15% SPVA-Li SPEs. The thermal stability of the solid polymer electrolyte directly determines the stability of the corresponding battery in operation. The TGA test can visually characterize the thermal decomposition temperature of the sample, as shown in FIG. 11, the decomposition temperature of both the 15% SPVA-Li SPEs and the PEO SPEs is higher than 250 ℃, which indicates that the PEO-based polymer electrolyte has better chemical stability at high temperature. To further characterize the thermal stability of both electrolytes, both electrolytes were baked on a hot stage at 100-150 ℃ for 10min and recorded. For comparison, a commercial polyolefin separator Celgard 2400 (abbreviated as PP) was tested as a control under the same conditions. From the photomicrograph of FIG. 4c, it can be seen that the 15% SPVA-Li SPEs can maintain shape integrity at 100 ℃. However, the shape of the PP separator and PEO SPEs deformed and shrunk. When the temperature is increased to 150 ℃, the shape of the PEO SPEs and PP separator is severely deformed and shrunk, which may induce contact between the positive and negative electrodes in practical use of the battery, eventually causing short-circuiting of the battery. In contrast, 15% SPVA-Li SPEs maintain shape integrity even at high temperatures of 150 ℃ and are of great importance in solid state, high safety batteries. The excellent high temperature resistance of the 15% SPVA-Li SPEs is mainly due to the fact that internal hydrogen bonds interact to form cross-linking, and therefore the thermal stability of the electrolyte is improved. Thus, 15% SPVA-Li SPEs are mechanically compared to PEO SPEsThe performance and the thermal stability are excellent, and the battery can be well ensured to be used under certain extreme conditions.

TABLE 1 summary of melting enthalpy, crystallinity and mechanical Properties of PEO SPEs and SPVA-Li SPEs

(III) characterization of electrochemical Properties of solid polyelectrolyte

Generally, the electrochemical stability of an electrolyte determines whether it can be used normally in a lithium battery. To test the stability of the electrolyte, the present invention tested the electrochemical stability window of 15% SPVA-Li SPEs and PEO SPEs at 60 ℃ by voltammetric scanning. As shown in FIG. 4d, the electrochemical stability window for PEO SPEs is only 4.1V narrower, while the 15% SPVA-Li SPEs have a wider electrochemical stability window (4.7V). The results indicate that the introduction of the SPVA-Li polymer filler into the PEO-based electrolyte can effectively improve the electrochemical stability of the electrolyte, thereby ensuring application in practical lithium batteries. In addition, the transference number of lithium ions is also an important electrochemical performance parameter for solid polymer electrolytes, and for Li⁺The efficiency of migration in the polymer is of great importance. The transference number of lithium ions is high, and concentration polarization in an electrolyte system can be reduced, so that the growth of lithium dendrites is inhibited. The lithium ion transference number of the solid polymer electrolyte can be obtained by combining a constant current method with EIS test and calculating according to a formula (3). The lithium ion transport number of the 15% SPVA-Li SPEs at 60 ℃ was calculated to be 0.59, a value significantly better than the PEO SPEs (0.39). The improvement of the transference number of lithium ions can be attributed to the following three factors: (1) low crystallinity and increased amorphous regions favor Li⁺The transmission of (1); (2) hydrogen bonding between SPVA-Li and PEO weakens the interaction of PEO and Li +, thereby releasing more Li⁺Carrying out transmission; (3) SPVA-Li as a single ion conductor polymer having a main chain containing a large amount of-SO capable of promoting the dissociation of lithium salt₃Thereby increasing Li⁺The efficiency of the transmission. Overall, 15% SPVA-Li SPEsThe electrochemical performance of the composite material is very superior to PEO SPEs, and the composite material has important significance in constructing high-performance lithium batteries.

To evaluate the compatibility of solid state polyelectrolytes and lithium metals, the present invention constructs and assembles a symmetrical battery Li | SPEs | Li at current densities of 25 and 50 μ A cm^-2And the temperature was 60 ℃. As shown in fig. 5a and b, the battery assembled using 15% SPVA-Li SPEs can be stably cycled for 400h without short circuit and polarization voltage increase during the entire cycle, indicating that the 15% SPVA-Li SPEs has good compatibility with lithium metal. In addition, the Li/Li symmetrical battery assembled by 15% SPVA-Li SPEs has smaller over-potential at 25 and 50 muA cm^-2The values of the overpotential at the lower points were 9 and 20mV, respectively. However, a symmetric Li/Li battery assembled using PEO SPEs was cycled for only 150h, and a short circuit occurred inside the battery, probably due to the eventual electrolyte puncture as lithium dendrites continued to form with cycling. To prove this hypothesis, the symmetric cell after the above cycle was disassembled, and the morphology of the lithium metal surface was observed by SEM test to confirm the magnitude of the inhibitory effect of different electrolytes on lithium dendrites. Fig. 12 shows that the surface of the lithium metal negative electrode before cycling was smooth and very tight. The lithium metal surface after cycling of the 15% SPVA-Li SPEs based cell was also relatively smooth with no lithium dendrite formation (fig. 5c, e and f). However, the lithium metal surface after cycling for the PEO SPEs cell was very rough and had significant lithium dendrite formation (fig. 5d, h and i). Thus, these results indicate that the 15% SPVA-Li SPEs have superior performance in inhibiting lithium dendrite growth over the PEO SPEs. The Li/Li symmetric battery assembled by 15% SPVA-Li SPEs has excellent long-term cycle performance mainly due to good compatibility with lithium metal, high lithium ion transport number and good mechanical performance. In order to test the application of the prepared solid polymer electrolyte in the actual solid lithium battery, LiFePO is adopted in the invention₄As a positive electrode, lithium metal is used as a negative electrode, 15% SPVA-Li SPEs and PEO SPEs are used as separators, and the lithium metal is assembled into LiFePO ₄15% SPVA-Li SPEs Li and LiFePO₄Both cells were subsequently tested. The interfacial properties of the electrolyte between the electrodes directly determine the cell's performanceRate capability and long-term cycling capability. The invention adopts EIS method to carry out reaction on LiFePO ₄15% SPVA-Li SPEs Li and LiFePO₄Both cells were tested for impedance at 60 ℃. The semi-circle of the impedance spectrum in fig. 6a represents the interfacial internal resistance between the electrolyte and the positive and negative electrodes, and LiFePO can be found₄The interfacial internal resistance of 15% SPVA-Li SPEs Li is only 30.3 Ω, which is much lower than 234.4 Ω for PEO SPEs based batteries under the same test conditions. Therefore, lower interfacial resistance is beneficial to the rate and cycling performance of the battery. The rate capability of the two cells was measured from 0.1C to 1C at 60C, cycling 5 cycles per rate. LiFePO as shown in FIG. 6b₄The 15% SPVA-Li SPEs Li battery has higher specific discharge capacity at 0.1, 0.2, 0.5 and 1C, which are specifically 166.8, 159.3, 131.6 and 115.5mA h g^-1The results are all higher than LiFePO₄The specific discharge capacity of the PEO SPEs Li battery under the same test conditions. In addition, the capacity-voltage curves of the fifth cycle at different magnifications are shown as a and b in fig. 13, and LiFePO can be found₄The 15% SPVA-Li SPEs Li battery has a flat and smooth charge-discharge platform under various multiplying powers, and the battery is shown to have good charge-discharge capacity reversibility. In contrast, LiFePO₄At higher rates of 1C, the charging platform operated unstably at high voltage due to the narrower electrochemically stable window of PEO electrolyte. Next, for LiFePO ₄15% SPVA-Li SPEs Li and LiFePO₄Both cells were tested for long-term cycling performance at 0.2 and 0.5C. As shown in FIG. 6C, LiFePO was present over the entire 0.2C cycle₄The 15% SPVA-Li SPEs Li battery can stably run for 100 cycles, and has higher specific discharge capacity and coulombic efficiency (close to 100%). In particular LiFePO₄The 15% SPVA-Li SPEs Li battery has 158.5mA h g in the first turn of 0.2C^-1Specific discharge capacity (close to LiFePO)₄Theoretical specific capacity) and a coulombic efficiency of 99.4%. After 100 cycles of charge/discharge at 0.2C rate, LiFePO₄The 15 percent SPVA-Li SPEs Li battery still keeps higher specific discharge capacity (129.1mA h g)^-181.5% of initial capacity) and better coulombic efficiency(98.4%). By way of comparison, LiFePO₄The PEO SPEs Li battery only circulates for 40 cycles, and the discharge specific capacity of the battery is from the initial 154.1mA h g^-1Reduced to 40.6mA h g^-1This is due to the fact that the continued growth of lithium dendrites during cycling pierces the electrolyte, causing a short circuit in the cell. Further, LiFePO₄The 15% SPVA-Li SPEs Li battery still has good circulation stability under the multiplying power of 0.5C, and still has 130.5mA h g after 100 cycles of circulation^-1The discharge specific capacity of the lithium ion battery is high, and the coulomb efficiency is very stable in the whole cycle. By way of comparison, LiFePO₄The | PEO SPEs | Li cell battery after 100 cycles at 0.5C despite having 122.7mA h g^-1The specific discharge capacity, but the coulombic efficiency fluctuates greatly after 70 cycles, indicating that side reactions occur in the presence of PEO SPEs that affect the electrochemical performance of the battery. Thus, the above results indicate that LiFePO was assembled using 15% SPVA-Li SPEs₄the/Li battery has excellent rate performance and long-term cycle performance because the electrolyte has excellent electrochemical and mechanical properties.

In conclusion, the invention successfully prepares the 15 percent SPVA-Li SPEs with flexibility, high mechanical strength and low crystallinity, and the electrolyte has high lithium ion transport number and conductivity. The polymer electrolyte is prepared by doping SPVA-Li serving as a polymer filler into a PEO SPEs system and then performing a solution casting method. The SPVA-Li and PEO in the polymer electrolyte have hydrogen bond interaction, so that the distribution of PEO molecules in the electrolyte is more disordered. On the one hand, the hydrogen bonding interaction can effectively inhibit the crystallization of polymer molecules, thereby effectively weakening O-Li⁺The ionic conductivity of the material is excellent (1.76 multiplied by 10)^-4S cm ^-160 ℃ C. On the other hand, the hydrogen bond crosslinking action can greatly improve the mechanical property and the thermal stability of the composite electrolyte. More importantly, the doped SPVA-Li has the behavior of a single-ion conductor, and can further improve the lithium ion transport number (0.59) of the composite electrolyte. Due to the improvement of electrochemical performance and mechanical performance, the Li/Li symmetrical battery has better long-term cycle performance when the electrolyte is used. Additionally, solid state LiFePO₄The electrolyte adopted by the Li battery has better rate performance and cycle performance than PEO SPEs. Therefore, the SPVA-Li/PEO composite polyelectrolyte prepared by the invention has a great application prospect in constructing high-performance and high-safety lithium batteries.

Claims

1. A preparation method of a hydroxyl-rich single-ion conductor polymer SPVA-Li is characterized by comprising the following steps: the method specifically comprises the following steps:

2. The method of preparing the hydroxyl-rich single-ion conductor polymer SPVA-Li of claim 1, wherein: the mass ratio of the polyvinyl alcohol to the 4-formyl benzene-1, 3-disodium disulfonate is 1: 1.5 to 2.

3. The method of preparing the hydroxyl-rich single-ion conductor polymer SPVA-Li of claim 1, wherein: the reaction temperature of the mixed reaction liquid is 70 ℃, and the stirring reaction time is 48 hours.

4. The method of preparing the hydroxyl-rich single-ion conductor polymer SPVA-Li of claim 1, wherein: the process adopted by the lithiation is as follows:

5. The hydroxyl-rich single-ion conductor polymer SPVA-Li prepared by the preparation method of the hydroxyl-rich single-ion conductor polymer SPVA-Li as claimed in any one of claims 1 to 4.

6. A preparation method of composite solid polymer electrolyte SPVA-Li SPEs is characterized in that: the method specifically comprises the following steps:

adding dried polyethylene oxide (PEO), lithium bistrifluoromethylsulfonate (LiTFSI) and the hydroxyl-rich single-ion conductor polymer SPVA-Li prepared by the method of any one of claims 1 to 4 into deionized water, and uniformly stirring to obtain a uniform viscous solution; and then pouring the viscous solution in a grinding tool, and drying after pouring to obtain the composite solid polymer electrolyte SPVA-Li SPEs.

7. The method of preparing a composite solid polymer electrolyte SPVA-Li SPEs according to claim 6, wherein: the mass ratio of the SPVA-Li to the PEO is 5-20: 100.

8. a composite solid polymer electrolyte SPVA-Li SPEs prepared by the method of claim 6 or 7.

9. Use of the composite solid polymer electrolyte SPVA-Li SPEs prepared by the method of claim 6 or 7 in a dendrite-free lithium metal battery or a solid lithium metal battery.

10. A dendrite-free lithium metal battery or a solid state lithium metal battery, comprising: comprising a composite solid polymer electrolyte prepared by the method of claim 6 or 7.